MojaSlovenija.si
MojaSlovenija.si |
GEO-X | |
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Literatura (sources):
Blockmeer, blockfield, block river, block run, everest, felsenmeer.
A blockmeer is a surface covered by block-sized angular rocks usually associated with alpine and subpolar climates and periglaciation. Blockfields differ from screes and talus slope in that blockfields do not apparently originate from mass movements.Most known blockfields are located in the northern hemisphere. Examples can be found in Abisko National Park in Sweden, Snowdonia National Park in Wales, and River of Rocks and Hickory Run Boulder Field in the Appalachian Mountains of the United States. All examples except the first one are outside present day subpolar climate areas, and have thus traditionally been seen as relict landforms from past times when these areas were under periglaciation.The term "felsenmeer" comes from the German meaning 'sea of rock'. In a felsenmeer (also known as a block field), freeze-thaw weathering has broken up the top layer of the rock, covering the underlying rock formation with jagged, angular boulders. Freeze-thaw weathering occurs when water that is trapped along microcracks in rock expands and contracts due to fluctuations in temperature above and below the freezing point. Felsenmeers are formed in situ, meaning that they are not transported during or after their creation.Blockmeer only form on slopes of 25° or lower. A steeper angle results in transport of the blocks due to gravity. This creates a talus slope, rather than a felsenmeer. Crude sorting with boulder imbrication can occasionally be seen on the surface of felsenmeers.Blockmeer is most often found in high mountain periglacial regions near the Arctic Circle, especially in Iceland, the Canadian arctic and Norway. Due to the slope requirements they are most commonly found on plateaus. Basalt and sedimentary rocks often produce larger, more numerous felsenmeers than other types of rock.It is a typically, relatively young geomorphological feature. Most blockmeer formed during or since the last ice age (approximately 20,000 years ago). Their specific age can be determined using surface exposure dating, a technique that works best on materials which have been exposed to cosmic rays with little interference from trees or soils.
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Izraz »blokmer« izhaja iz nemškega izraza Blockmeer (tudi Felsenmeer), kar v dobesednem prevodu pomeni 'morje skal'. Blokmer je pojav kjer se je gornja plast kamnine v obliki kamniti blokov različnih dimenzij zaradi periglacialnih procesov odlomila od matične kamnine. Debelina 'odlomljene' plasti skal od matične kamnine je odvisna od kota pobočja, vrste kamnine in časa delovanja periglacialnih procesov. Drobnejši odlomljeni material je podvržen drugim denudacijskim procesom, zato se večje skale podobnih velikosti formirajo na skupnem območju in med njimi ni drobnejšega materiala. Blokmer se pojavi na pobočjih s kotom manjšim od 25°. Večina blokmerjev se je formiralo v času zadnje ledene dobe pred 20.000 leti. Čeprav lahko blokmerje najdemo tudi v tropskih klimatskih pogojih, kjer je prisotno globoko kamninsko preperevanje, so najpogostejši na območjih kjer so prisotni periglacialni procesi – gorska ali subpolarna območja z magmatskimi ali metamorfnimi kamninami. V Sloveniji so blokmeri prisotni na Pohorju na pobočjih doline reke Lobnice.
